# 作业先完成，再完美
# create 增
# INSERT INTO test(tel, gender, money, float_field, double_field) VALUES('12345678901', '男', 123, 12345.12, 123456789.12), ('9876543210', '女', 456, 54321.12, 987654321.12)

# 查全部
# SELECT * FROM test
# 条件查询
# SELECT gender FROM test WHERE gender = '女' AND id = 4 OR id = 5
# 模糊查询
# SELECT money FROM test WHERE money LIKE "%2%"
# 限制返回条数
# SELECT * FROM test WHERE gender = '女' LIMIT 2
# 过滤重复值
# SELECT DISTINCT gender FROM test
# 排序
# SELECT * FROM test ORDER BY id DESC
# 计数
# SELECT COUNT(*) FROM test

# UPDATE
# UPDATE test SET gender = '未知' WHERE id = 5

# DELETE
# DELETE FROM test WHERE id = 4


# 集合操作
# SELECT name FROM class_1 WHERE name is not NULL
# UNION
# SELECT name FROM class_2 WHERE name is not NULL
#
# SELECT A.name FROM
# (SELECT name FROM class_1 WHERE name is not NULL) as A
# JOIN
# (SELECT name FROM class_2 WHERE name is not NULL) as B
# ON A.name=B.name
#
# SELECT A.name FROM
# (SELECT name FROM class_1 WHERE name is not NULL) as A
# LEFT JOIN
# (SELECT name FROM class_2 WHERE name is not NULL) as B
# ON A.name=B.name
# WHERE B.name is NULL
#
# UNION
#
# SELECT B.name FROM
# (SELECT name FROM class_1 WHERE name is not NULL) as A
# RIGHT JOIN
# (SELECT name FROM class_2 WHERE name is not NULL) as B
# ON A.name=B.name
# WHERE A.name is NULL
